GHSA-W825-9XQR-F6Q3
Vulnerability from github – Published: 2024-05-21 15:31 – Updated: 2024-12-26 21:30In the Linux kernel, the following vulnerability has been resolved:
bpf: Track subprog poke descriptors correctly and fix use-after-free
Subprograms are calling map_poke_track(), but on program release there is no hook to call map_poke_untrack(). However, on program release, the aux memory (and poke descriptor table) is freed even though we still have a reference to it in the element list of the map aux data. When we run map_poke_run(), we then end up accessing free'd memory, triggering KASAN in prog_array_map_poke_run():
[...] [ 402.824689] BUG: KASAN: use-after-free in prog_array_map_poke_run+0xc2/0x34e [ 402.824698] Read of size 4 at addr ffff8881905a7940 by task hubble-fgs/4337 [ 402.824705] CPU: 1 PID: 4337 Comm: hubble-fgs Tainted: G I 5.12.0+ #399 [ 402.824715] Call Trace: [ 402.824719] dump_stack+0x93/0xc2 [ 402.824727] print_address_description.constprop.0+0x1a/0x140 [ 402.824736] ? prog_array_map_poke_run+0xc2/0x34e [ 402.824740] ? prog_array_map_poke_run+0xc2/0x34e [ 402.824744] kasan_report.cold+0x7c/0xd8 [ 402.824752] ? prog_array_map_poke_run+0xc2/0x34e [ 402.824757] prog_array_map_poke_run+0xc2/0x34e [ 402.824765] bpf_fd_array_map_update_elem+0x124/0x1a0 [...]
The elements concerned are walked as follows:
for (i = 0; i < elem->aux->size_poke_tab; i++) {
poke = &elem->aux->poke_tab[i];
[...]
The access to size_poke_tab is a 4 byte read, verified by checking offsets in the KASAN dump:
[ 402.825004] The buggy address belongs to the object at ffff8881905a7800 which belongs to the cache kmalloc-1k of size 1024 [ 402.825008] The buggy address is located 320 bytes inside of 1024-byte region [ffff8881905a7800, ffff8881905a7c00)
The pahole output of bpf_prog_aux:
struct bpf_prog_aux { [...] / --- cacheline 5 boundary (320 bytes) --- / u32 size_poke_tab; / 320 4 / [...]
In general, subprograms do not necessarily manage their own data structures. For example, BTF func_info and linfo are just pointers to the main program structure. This allows reference counting and cleanup to be done on the latter which simplifies their management a bit. The aux->poke_tab struct, however, did not follow this logic. The initial proposed fix for this use-after-free bug further embedded poke data tracking into the subprogram with proper reference counting. However, Daniel and Alexei questioned why we were treating these objects special; I agree, its unnecessary. The fix here removes the per subprogram poke table allocation and map tracking and instead simply points the aux->poke_tab pointer at the main programs poke table. This way, map tracking is simplified to the main program and we do not need to manage them per subprogram.
This also means, bpf_prog_free_deferred(), which unwinds the program reference counting and kfrees objects, needs to ensure that we don't try to double free the poke_tab when free'ing the subprog structures. This is easily solved by NULL'ing the poke_tab pointer. The second detail is to ensure that per subprogram JIT logic only does fixups on poke_tab[] entries it owns. To do this, we add a pointer in the poke structure to point at the subprogram value so JITs can easily check while walking the poke_tab structure if the current entry belongs to the current program. The aux pointer is stable and therefore suitable for such comparison. On the jit_subprogs() error path, we omit cleaning up the poke->aux field because these are only ever referenced from the JIT side, but on error we will never make it to the JIT, so its fine to leave them dangling. Removing these pointers would complicate the error path for no reason. However, we do need to untrack all poke descriptors from the main program as otherwise they could race with the freeing of JIT memory from the subprograms. Lastly, a748c6975dea3 ("bpf: propagate poke des ---truncated---
{
"affected": [],
"aliases": [
"CVE-2021-47303"
],
"database_specific": {
"cwe_ids": [
"CWE-416"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-05-21T15:15:18Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Track subprog poke descriptors correctly and fix use-after-free\n\nSubprograms are calling map_poke_track(), but on program release there is no\nhook to call map_poke_untrack(). However, on program release, the aux memory\n(and poke descriptor table) is freed even though we still have a reference to\nit in the element list of the map aux data. When we run map_poke_run(), we then\nend up accessing free\u0027d memory, triggering KASAN in prog_array_map_poke_run():\n\n [...]\n [ 402.824689] BUG: KASAN: use-after-free in prog_array_map_poke_run+0xc2/0x34e\n [ 402.824698] Read of size 4 at addr ffff8881905a7940 by task hubble-fgs/4337\n [ 402.824705] CPU: 1 PID: 4337 Comm: hubble-fgs Tainted: G I 5.12.0+ #399\n [ 402.824715] Call Trace:\n [ 402.824719] dump_stack+0x93/0xc2\n [ 402.824727] print_address_description.constprop.0+0x1a/0x140\n [ 402.824736] ? prog_array_map_poke_run+0xc2/0x34e\n [ 402.824740] ? prog_array_map_poke_run+0xc2/0x34e\n [ 402.824744] kasan_report.cold+0x7c/0xd8\n [ 402.824752] ? prog_array_map_poke_run+0xc2/0x34e\n [ 402.824757] prog_array_map_poke_run+0xc2/0x34e\n [ 402.824765] bpf_fd_array_map_update_elem+0x124/0x1a0\n [...]\n\nThe elements concerned are walked as follows:\n\n for (i = 0; i \u003c elem-\u003eaux-\u003esize_poke_tab; i++) {\n poke = \u0026elem-\u003eaux-\u003epoke_tab[i];\n [...]\n\nThe access to size_poke_tab is a 4 byte read, verified by checking offsets\nin the KASAN dump:\n\n [ 402.825004] The buggy address belongs to the object at ffff8881905a7800\n which belongs to the cache kmalloc-1k of size 1024\n [ 402.825008] The buggy address is located 320 bytes inside of\n 1024-byte region [ffff8881905a7800, ffff8881905a7c00)\n\nThe pahole output of bpf_prog_aux:\n\n struct bpf_prog_aux {\n [...]\n /* --- cacheline 5 boundary (320 bytes) --- */\n u32 size_poke_tab; /* 320 4 */\n [...]\n\nIn general, subprograms do not necessarily manage their own data structures.\nFor example, BTF func_info and linfo are just pointers to the main program\nstructure. This allows reference counting and cleanup to be done on the latter\nwhich simplifies their management a bit. The aux-\u003epoke_tab struct, however,\ndid not follow this logic. The initial proposed fix for this use-after-free\nbug further embedded poke data tracking into the subprogram with proper\nreference counting. However, Daniel and Alexei questioned why we were treating\nthese objects special; I agree, its unnecessary. The fix here removes the per\nsubprogram poke table allocation and map tracking and instead simply points\nthe aux-\u003epoke_tab pointer at the main programs poke table. This way, map\ntracking is simplified to the main program and we do not need to manage them\nper subprogram.\n\nThis also means, bpf_prog_free_deferred(), which unwinds the program reference\ncounting and kfrees objects, needs to ensure that we don\u0027t try to double free\nthe poke_tab when free\u0027ing the subprog structures. This is easily solved by\nNULL\u0027ing the poke_tab pointer. The second detail is to ensure that per\nsubprogram JIT logic only does fixups on poke_tab[] entries it owns. To do\nthis, we add a pointer in the poke structure to point at the subprogram value\nso JITs can easily check while walking the poke_tab structure if the current\nentry belongs to the current program. The aux pointer is stable and therefore\nsuitable for such comparison. On the jit_subprogs() error path, we omit\ncleaning up the poke-\u003eaux field because these are only ever referenced from\nthe JIT side, but on error we will never make it to the JIT, so its fine to\nleave them dangling. Removing these pointers would complicate the error path\nfor no reason. However, we do need to untrack all poke descriptors from the\nmain program as otherwise they could race with the freeing of JIT memory from\nthe subprograms. Lastly, a748c6975dea3 (\"bpf: propagate poke des\n---truncated---",
"id": "GHSA-w825-9xqr-f6q3",
"modified": "2024-12-26T21:30:35Z",
"published": "2024-05-21T15:31:42Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2021-47303"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/599148d40366bd5d1d504a3a8fcd65e21107e500"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a9f36bf3613c65cb587c70fac655c775d911409b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f263a81451c12da5a342d90572e317e611846f2c"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.